1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for dynamically allocating radio resources in a broadband wireless communication system.
2. Description of the Related Art
Next generation communication systems provide users with mobility and various services based on a Wireless Local Area Network (WLAN) or a Wireless Metropolitan Area Network (WMAN) at a high data transfer rate.
The communication system may use an Orthogonal Frequency Division Multiple Access (OFDMA) scheme. In the OFDMA scheme, data may be transmitted by dividing a frequency band to be used into several small frequency bands (i.e., subchannels and timeslots). That is, since a plurality of subchannels are used to transmit physical channel signals, data may be transmitted at a high speed. In addition, the OFDMA scheme is robust to frequency-selective fading.
When using the OFDMA scheme, a usage rate of radio resources may be increased according to a manner of distributing slots to Access Terminals (ATs). The slots are radio resources which are divided in a frame into subchannels and timeslots. The slot is a basic unit of resource allocation. A group of a plurality of consecutive slots may be defined as a radio resource for data burst allocation. In this case, a Base Station (BS) determines a manner of distributing the radio resources to the ATs in every frame, and informs the determination result to the ATs by using a resource allocation message (i.e., a MAP message).
A method of allocating bitmap resources is a technique for reducing overhead according to the resource allocation message. That is, when radio resources are dynamically allocated to a plurality of ATs, the BS matches the respective ATs to bits of a bitmap in a one-to-one manner. The bits of the bitmap are set to ‘0’ or ‘1’ to indicate whether the radio resources are allocated to the respective ATs. Since the BS uses a short-length bitmap format to identify the ATs allocated with the radio resources instead of using AT IDentifier (IDs), there may be an advantage in that more radio resources may be ensured for data communication.
FIG. 1 illustrates a conventional method of allocating and deallocating bitmap resources. Referring to FIG. 1, ATs A, B, C, and D respectively and sequentially correspond to bits of a bitmap. When radio resources are allocated to the ATs A, B, and D in step 102, the bitmap included in a resource allocation message may be expressed by ‘1101’. If the AT B no longer needs to be allocated with the bit of the bitmap and if a new AT E needs to be allocated with the bitmap, a bitmap deallocation message and a bitmap allocation message are transmitted respectively in steps 104 and 108 to the AT B and the AT E. A feedback signal (i.e., acknowledgement (ACK) or Negative ACK (NACK)) may then be received respectively in steps 106 and 110 from the AT B and the AT E. Thereafter, in step 112 a resource allocation message including a new bitmap expressed by ‘0110’ may be transmitted. In the above described case, a unicast message may be used for bitmap allocation and deallocation, which leads to an increase in a waste of radio resources for bitmap management.
In other words, a method in which bit positions of a bitmap are informed to respective ATs by using separate messages in a unicast manner results in low efficiency when the bit positions are modified. In the method of allocating bitmap resources, a bit allocated to an AT for which resource allocation is no longer necessary may be immediately allocated to another AT in order to maintain a short-length bitmap. However, separate messages are used for bit allocation and deallocation of the bitmap and are transmitted in a unicast manner in the conventional method. Therefore, there may be a waste of radio resources that results from bitmap management.